Electrode for gaseous discharge devices



Sept. 28, 1943. I w. v. SMITH 2,330,248

ELECTRODE FOR GASEOUS DISCHARGE DEVICES Filed Jan. 50, 1942 WilliammithINVENTOR.

r A TTORNEY Patented'Sept. 28, 1943 William v. Smith, Salem, Mass,assignor to Sylvania Electric Products Inc., a corporatio ofMassachusetts Application January 30, 1942, Serial No. 428,887 4 Claims.(Cl. its-12c) This invention relates to electric gaseous discharge lampsand-more particularly to cathodes therefon,

An object of this invention is to provide a cathode of such a structurethat the lamp in which it is used will have a relatively long life.

Another object is to provide a cathode capable of being readily adaptedto cold starting conditions with a minimum of deleterious eflects.

A further object is to provide a cathode of such a structure that suchconditions as sputter will be greatly eliminated.

Further objects; advantages and features will be apparent from thefollowing specification taken in conjunction with the accompanyingdrawing in which:

Figure 1 is a side elevational view partly cut away to show the cathodestructure.

Figure 2 is an end view showing the coiledcoiled filamentary wire withinthe coiled wire.

In the manufacture of electric gaseous discharge lamps of the type withone or more electrodes having electron emissive materialit has beenfound that one of the factors which affect the life of the lamp is thedisintegration of the electron-emissive material. I have thereforedevised a cathode capable of carrying a large quantity of electronemissive material considerably shielded and protected from the path ofthe discharge.

The lead-in wires l and 2 extending up through the glass mount 3 havethe outer coil 4 mounted between the ends thereof. The coiled-coiledwire 5 is located within the turn of the outer coil 4 as shown in thecut-away portion of Figure 1 and in the end view of Figure 2.

If the inner coil 5 is of considerably higher resistance than the outercoil 4, it is immaterial whether they are connected at their ends or notfor the difference in resistances plus the dinerence in pitch of the twocoils will prevent any substantial short-circuiting from taking place.If the innercoil is of about the same resistance as the outer coil it ispreferable to join the ends of the inner coil to the outer coil. Ineither case if the inner coil touches the outer at several points alongtheir longitudinal axis the practical result will be a series ofparallel resistors having the same eifective resistance as the parallelresistance of the two coils. 1

The electron-emissive material may be applied to the coiled-coiled wirebefore it is inserted within the outer coil and then a secondapplication of electron-emissive material be made. However, I have foundit more advantageous to locat the coiled-coiled wire within the outercoil first and then apply the electron-emissive material thereto. Thismay be done in the manner described in U. S. Patent No. 2,258,158 issuedOctober 7, 1941, whereby the material is closely held in a uniformmanner.

A structure of this type provides considerable protection of theelectron-emissive material from the positive ion bombardment. The outercoil, being closely wound, shields the inner coiledcoiled wire and themain body of the electronemissive material. Thus sputtering of thecoating is cut down considerably. This shielding not only p fevents theflying ofi of particles of the electron-emissive material and thecollection thereof on the walls of the lamp but it also protects theelectron-emissive material from the discharge under cold startingconditions.

It may be noted that if coils 4 and 5 are both connected to the lead-inwires, the discharge may go to either coil, depending, at least in part,on which coil retains the most active cathode coating. With the outercoil closely wound the inner coil and the electron-emissive material isshielded and .thus no substantial amount of sputtering takes place. Suchsputtering as might take place is not sufficient to discolor the wallsof the lamp and is just about enough to keep the outer coil active.

What I claim is:

1. An electrode assembly for an electric gaseous discharge devicecomprising: a pair of leading each end connected to one of said lead-inwires; an inner, coiled-coiled filamentary wire having a major and aminor coil and located within the coils of said outer wire; and afilling of electronemissive material within and between the turns ofsaid major and minor coils and within the turns of said outer coil.

2. An electrode assembly for an electric gaseous discharge devicecomprising: a coiled filamentary wire, a second coiled filamentary wireof a difierent degree of pitch than said first wire, said second wirebeing located within the coils of said firstwire and disposed along thelongitudinal axis thereof; and a filling of electronemissive materialwithin the turns of said first wire, and within and between the turns ofaid second wire in such manner as to fill the space within the turns of,and to envelop, said second wire.

3. An electrode assembly for an electric gaseous discharge devicecomprising: a coiled filamentary wire; a second coiled filamentary wirea different pitch than said first wire, said second wire being locatedwithin the coils 01. said first wire and disposed along the longitudinalaxis thereof; and a filling of electron-emissivematerial within theturns of said first wire, within the turns of said second wire andenveloping said second wire; said second wire having a resistancesubstantially higher than the resistance of the first wire.

WILLIAM V. SMITH.

